Concepts concerning the dietary factors that influence HDL metabolism are particularly complex since this lipoprotein class contains at least two major subclasses, i.e., HDL2 and HDL3. Reports are conflicting concerning the apparent significance of the relative proportions of these two subclasses especially as they relate to hyperlipidemia and risk to atherosclerosis. Utilizing two monkey models with contrasting levels of HDL subclasses, i.e., the squirrel monkey (HDL2 greater than HDL3) and cebus monkey (HDL2 less than HDL3), an in vitro liver perfusion system will be employed for assessing HDL subclass synthesis and HDL subclass uptake by monkey livers as well as the transfer of cholesterol from either HDL subclass or apoE-rich HDL into biliary cholesterol and bile acids. In addition, the activity of cholesteryl ester transfer protein, lecithin:cholesteryl acyltransferase, hepatic lipase and lipoprotein lipase will be correlated with species and diet-induced variations in HDL2-HDL3 levels. Investigation of these objectives will identify specific factors that regulate HDL subclass levels and enhance our understanding of their association with specific disease states.